Please note: This information was current at the time of publication but now may be out of date. This handout provides a general overview and may not apply to everyone. 

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Am Fam Physician. 1999;60(3):756-757

See related Medicine and Society on genetic testing.

What are genes and how are they related to disease?

Genes are long molecules called DNA that are present in every cell in your body. DNA controls growth and helps you stay healthy. If your DNA is abnormal or damaged, it may not work properly, which may lead to disease. Some genetic abnormalities, or “gene mutations,” may run in families. Some just happen by chance. Sometimes one mutation may cause a person to have a disease, but most diseases are caused by a combination of genetic and environmental factors.

What is genetic testing?

Genetic testing may help to show if you've inherited a tendency to get certain diseases. A sample of blood or skin is usually needed for genetic testing. Genetic testing for mutations is slowly becoming available. However, many doctors still don't know a lot about the tests and how to use them.

What does a positive result mean?

A positive test result means that you have the mutation you've been tested for. If you have a positive test result, it means you may be more likely to get the disease than most people, but it doesn't mean you will definitely get the disease.

What does a negative result mean?

A negative test result means that you don't have that particular mutation. This may mean that the disease doesn't run in your family, or it may mean that some other gene causes the disease. A negative result doesn't mean you won't get the disease. It only means that you're not more likely to get the disease than other people.

Who should be tested?

By looking at your family history, your doctor can tell if you're likely to have a gene mutation that may contribute to disease. A disease might run in your family if a relative developed the disease at a young age, or if several family members have the disease or if the condition is rare. People from certain ethnic groups may also be more likely to get certain diseases. If one of your family members already has the disease, that person should be tested first. This helps show which genes, if any, are associated with the disease.

How do I decide if I should get tested?

If you think you may be at high risk for an inherited disease, talk to your family doctor. Your doctor will ask you questions about your health and the health of your blood relatives. This information will help your doctor to see what your risks might be. The information your doctor gives you about your risks can help you decide whether you want to be tested.

There are two important questions you should think about before you go through genetic testing:

1. What can I gain by being tested?

Specific medical recommendations vary with the type of disease. Here are some reasons why you might want genetic testing:

  • You might not be so worried about getting a disease.

  • You might be able to change your diet or start exercising to reduce your risk of getting a disease.

  • Your doctor will know how often to check you to see if you're getting a disease.

  • You might be able to take medicine to prevent the disease.

2. Are there any negative effects of testing?

You might not want to know that you may be at risk for a certain disease because of these reasons:

  • Testing may make you more worried about getting sick.

  • Testing may give you stress, make you feel guilty, or strain your family relationships.

  • Testing could lead to problems with employers or insurance companies.

How can I find out more about genetic testing for disease?

To find out more about genetic testing, you may want to contact one of the following organizations:

  • The National Society of Genetic Counselors

    Telephone: 610-872-7608, press 7

    Web site: and click on “Resource Link”)

  • The National Cancer Institute

    Telephone: 800-4CANCER

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